The present invention relates generally to the packaging of multichip integrated circuit modules. More particularly, it relates to the use of bonding wires that cross one another to connect integrated circuits in a multi-chip package.
Semiconductor integrated circuits are currently mass produced for a broad range of purposes. Therefore, cost and quality improvements in their manufacturing are valuable since even small savings in the costs of packaging can translate to large overall cost savings when mass produced.
In recent years, the popularity of multichip modules (MCM's) or multichip packages (MCP's) that contain more than one integrated circuit die has increased because they provide the convenience of complex components composed of several simpler integrated circuits. The terms multichip module and multichip package will be considered synonymous throughout this application. One drawback of multichip modules is that they may require complicated bonding wire topographies to connect the dies to external leads or to each other or to, both. In the past, a variety of techniques have been used to accomplish these interconnections. Referring next to FIGS. 1a-1d, a variety of known MCM wire bonding techniques will be described.
Referring initially to FIG. 1a a simple bonding wire arrangement for a conventional multichip module 10 is illustrated. Integrated circuit dies 12 are attached to die attach pads 14 of a lead frame. Bonding wires 16 electrically connect the dies 12 to external leads 18 of the lead frame. In this embodiment, the various dies are not connected together in any way. Although this type of multichip module is simple and inexpensive to produce, there are often times when it is necessary to interconnect the dies. Indeed it is usually necessary to interconnect the dies in order to make full use of the benefits of multichip packaging.
An improvement is shown in FIG. 1b wherein the bonding wires 16 connect the dies 12 to each other in addition to the external leads 18. However, to prevent the bonding wires from shorting one another, the bonding wires are not crossed in any way. Although some interconnection is allowed using this approach, the inability to cross the bonding wires significantly restricts the number of connections that can be made between adjoining dies. Clearly, the desire for more complicated wiring topographies is easily imagined. To circumvent this problem, some manufacturers connect the dies via traces that pass through the substrate. Alternatively, a jumper chip may be provided to facilitate the connections. FIGS. 1c and 1d show these two alternatives.
In FIG. 1c, the dies 12 are on the mounted on a substrate 20. The substrate 20 has a plurality of surfaces traces 22. There are also a variety of submerged traces that run through the substrate. The dies can then be connected by wire bonding between a first die and a first end of a trace on the substrate using a first bonding wires 16 and then wire bonding between a second die and a second end of the trace. In this manner good connections can be made without crossing the bonding wires which again would risk shorting. Similarly, as seen in FIG. 1d a jumper chip 24 may be provided in place of or in addition to the traces that run through the substrate to facilitate connections between the dies. The jumper chip 24 has a multiplicity of traces 26 which can be accessed by the bonding wires 16 without requiring any of the bonding wires to cross. Unfortunately, the substrate and jumper chip solutions are expensive. Indeed, when substrates or jumper chips are used, they account for most of the cost of MCM manufacture. The design of the submerged substrate connections and their implementation are also complicated. Accordingly, a simple, inexpensive method permitting crossed bonding wires without shorting would thus be desirable.